• 4.1 baseline — 0.6 × season 3.6 (5 gm) + 0.4 × last 10 4.9
• +0.6 opponent leak — they concede 106.2/game vs a 93.4 league average
• −0.5 at this ground — averages 3.6 there (7 gm)
• vs them: averages 4.8 over 8 games — evidence, never summed

Derived, not measured — plain arithmetic over his real games, shown in full. Adjustments can overlap (a game at this ground can also be a wet one); they add simply, and this note is the admission.